1) Field of the Invention
The present invention relates generally to agricultural implements and, more specifically, to an improved and simplified spring trip standard for tillage implements.
2) Related Art
Spring trip standards typically include a mounting bracket attached to rectangular toolbar and extending upwardly and rearwardly to a downwardly and forwardly directed spring abutment surface. A spring is compressed between the abutment surface and an upwardly directed spring abutment surface on a member pivotally connected to the lower portion of the bracket, and a tool supporting shank is fixed to the member. A tension link assembly extends from the shank supporting member through the spring and through an aperture in the spring abutment surface on the bracket to adjust the preloading of the spring and vary the vertical position of the tool connected to the shank. Such an assembly is shown by way of example in U.S. Pat. No. 3,700,039 entitled SPRING TRIP SHANK ASSEMBLY. Such a shank assembly provides good trip force characteristics but has numerous parts and is expensive and time-consuming to assemble and repair. Previously available assemblies, particularly those with numerous tension link or spring support components such as pins, straps, spacers and washers, typically require extensive instructions for assembly and disassembly. In some shank assemblies, the tension link reduces forces on the pivot area in the at rest position, thereby introducing some looseness in the pivot joints which often is perceived as a quality disadvantage and which causes the tool to have some lateral shift during operation. Often the precompression of the spring when the tool is in the normal operating position is not sufficient to prevent some continual tripping action. The portion of the tension link extending through the aperture is subject to wear as a result of such tripping action.
In some spring trip shank assemblies such as shown in U.S. Pat. No. 4,520,878 the bottom of the coil spring rests on a seat which can swivel to maintain the lower face of the spring substantially normal to the longitudinal axis of the spring and thereby reduce spring buckling forces. Such arrangements require numerous components and are relatively difficult to assemble. The swiveling seat construction introduces additional wear components into the assembly.